In a mechanical seal serving as one example of the sliding parts, performances thereof are evaluated by a leakage amount, a wear amount, and torque. In the prior art, the performances are enhanced by optimizing sliding material and sealing face roughness of the mechanical seal, so as to realize low leakage, long life, and low torque. However, due to raising awareness of environmental problems in recent years, further improvement in the performances of the mechanical seal is required, and there is a need for technical development going beyond the boundary of the prior art.
Under such circumstances, the present applicant filed an application for a patent on the invention of sliding parts in which no leakage is caused in a static state, the sliding parts that are actuated with fluid lubrication in a rotating state including an initial stage of rotation while leakage is prevented, so that sealing and lubrication can be realized at the same time (hereinafter, referred to as the “prior art”, see Patent Document 1).
As one embodiment of this prior art, as shown in FIG. 5, sliding parts in which an outer peripheral side of a sliding part 31 including annular bodies serves as a high pressure fluid side and an inner peripheral side serves as a low pressure fluid side, a groove section 35 of a Rayleigh step mechanism 33 that forms a positive pressure generation mechanism is provided on a high pressure side of a sealing face 32, a groove section 36 of a reversed Rayleigh step mechanism 34 that forms a negative pressure generation mechanism is provided on a low pressure side, a pressure release groove 45 is provided between the groove section 35 and the groove section 36, and the groove section 35, the pressure release groove 45, and the groove section 36 communicate with the high pressure fluid side via a radial groove 37 and are isolated from the low pressure fluid side by a seal face 38, wherein the radial groove 37 is inclined toward the rotating direction of the opposing sealing face from the inner peripheral side where the radial groove communicates with the groove section 36 toward the outer peripheral side are proposed. In a case of this embodiment, a fluid on the sealing face 32 is discharged in the direction shown by an arrow 46. The groove depth of the groove section 35 and the groove section 36 is about a few nm, the groove depth of the radial groove 37 and the pressure release groove 45 is about ten μm, and the groove depth of the radial groove 37 and the pressure release groove 45 is sufficiently greater than the groove depth of the groove section 35 and the groove section 36.